Anodes for capacitors, especially capacitors utilizing aluminum as valve metal, are well known in the art. Bourgault et al. describe in U.S. Pat. No. 3,345,545 a capacitor with a solid porous anode. Evans et al. describe in U.S. Pat. No. 6,721,170 a basic capacitor design with a bulky anode that casing be made from either tantalum or aluminum. In U.S. Pat. No. 7,342,744 Hossick-Schott et al. describe a slug anode which casing be made from aluminum or tantalum. Also disclosed is the use of a cross-sectional density gradient.
In U.S. Pat. No. 3,113,376, Pflumm et al. describe an alloying process which involves brittle materials.
Although the prior art describes many possibilities for producing anodes for capacitors, there is still a need for anodes for capacitors with a high energy density for special applications such as, but not limited to, high voltage capacitors. Beside the well known applications like flashbulbs, these capacitors are of increasing interest due to its applications (or possible applications) in the automotive sector, in scientific equipment and in medical devices, like defibrillators or cardioverters-defibrillators. In implantable devices it is particularly useful to obtain a high energy density, which allows smaller or more efficient devices. Slug anodes are nowadays made from sintered powder, with tantalum powder being particularly dominant. The sintered porous materials used for anodes, mainly valve metals like tantalum or aluminum, exhibit a large effective surface area, which is necessary for the high energy density. Therefore tantalum and aluminum are prominent materials used for capacitors in implantable medical devices. Beside the slug anode configuration there are other configurations like stacked electrodes or rolled electrodes, which both lack either high energy density or the possibility for a compact design. The standard method for producing slug anodes from powder material is difficult to handle for aluminium, and thus has not been of use up to now. Therefore a method to overcome that problem, and to produce aluminum slug anodes for high energy density capacitors, is needed.